1. Field of the Invention
The present invention relates to (1) a polymer containing specific repeating units, (2) a resist material comprising the polymer, and (3) a patterning process using the resist material.
2. Description of the Related Art
In recent years, along with the trend toward higher integration and higher operation speed of LSI devices, there has been a demand for a finer pattern rule. Under such a situation, deep-ultraviolet lithography is considered promising as next generation microfabrication technology. In particular, photolithography using KrF or ArF excimer laser as a light source is eagerly desired to reach the practical level as a technique indispensable for microfabrication to a feature size of 0.3 μm or less.
Resist materials for KrF excimer laser in fact contain, as a standard base resin, polyhyroxystyrene imparting a practical level of transparency and etching resistance. For resist materials for ArF excimer laser, on the other hand, polymers using a polyacrylic or polymethacrylic acid derivative containing an adamantane structure in the side chain thereof tend to be used as described in Japanese Patent Application Unexamined Publication Nos. 9-73173/1997 and 9-90637/1997. However, few of these polymers exhibit their performance fully.
Although sensitivity and dry etching resistance can be improved to some extent by introducing many adamantane-structure-containing acid reactive groups typified by a 2-alkyl-2-adamanthyl group, the resin as a whole inevitably becomes very adamant and hydrophobic owing to the inflexibility and hydrophobicity of the adamantane structure. Such adamant and highly hydrophobic resist materials may cause peeling of a resist film due to lowering in the substrate adhesion, development defects due to lowering in the affinity with a developer, and deterioration in solubility in an all-purpose resist solvent such as propylene glycol monomethyl ether acetate. In addition, although highly hydrophobic resist materials can persistently keep a film in the unexposed portion and dissolve the film speedily in the over-exposed portion, affinity with a developer is insufficient in a considerably wide exposed portion between the portions so that the film fails to dissolve in a developer, causing swelling of the resist film upon development. As a result, this impairs the resolution or convenience, for example, through adhesion or collapse of patterns, roughening on the side walls of the patterns, or fluctuations in the size due to slight unevenness in the heat treatment temperature after exposure. Since a demand for finer pattern rule is high in future, such a resist material cannot be developed to a practical level. Under such a tendency, there is accordingly a demand for a resist material which has excellent performance in affinity with a developer, sensitivity and resolution and can be of easy use owing to a wide range of processing conditions, while having dry etching resistance enough for practical use.